On heavy road vehicles, bosses, trailers and similar drum brakes as well as disc brakes are employed which comprise brake lever, respectively. For example, disc brakes with a corresponding lever arrangement are known from EP 0 553 105 B1 or WO 2004/059187 A1 of the applicant. However, the invention in particular concentrates on drum brakes in which the brake lever attaches an S-camshaft and which comprises a housing which receives an automatic brake (or slack) adjuster, as this is exemplarily disclosed in EP 0 598 290 B1 and EP 1 064 472 B1 of the applicant or in U.S. Pat. No. 3,392,810.
The brake lever for such drum brakes serves to transform the linear movement of a rod from a pneumatic or hydraulic actuator to a rational movement of a shaft of such a drum brake assembly in order to apply with the brake linings of the brake shoes during brake actuation. The brake lever itself is preferably made as one piece and comprises a housing section into which an automatic slack adjuster arrangement is received in order to provide compensation of the wear of the brake shoes of the drum brake. With respect to the exact functioning of the automatic slack adjuster arrangement and brake lever in this context it is, for example, referred to EP 0 598 290 B1 of the applicant.
The brake lever thus have to be considered as being the crucial component of the entire arrangement with respect to the dynamic and static applied loads as present in such a drum brake. Generally, the brake lever is configured as an elongated device with a housing section into which the automatic slack adjuster arrangement is inserted, and with a lever section which comprises a free end being connected with the actuator.
So far, the brake lever and in particular the housing for receiving the brake adjuster normally have been made of spheroidal graphite cast iron, which is existing with different ferritic and pearlitic grades, which means that the base material of the cast iron consists of ferrite to pearlite. Spheroidal graphite in this context means that the free carbon is formed embedded in a ferrite- and/or pearlite matrix in spherical, i.e. globular or nodular form. At this it is a specific form of deposition of the carbon in a spherical form, i.e. as compared to steel, carbon is not directly embedded in the elementary cell of the iron but forms differently shaped faces of graphite within the alloy.
Herewith a larger percentage of pearlite in the matrix provides an increased hardness and strength, while a larger percentage of ferrite deals a better ductility and better machining properties.
Instead of cast iron the housing of brake lever according to the prior art can be also made of forged steel.
The housing or the housing section of the brake lever in which the slack adjuster arrangement is arranged comprises several internal surface sections which are supposed to large contact pressure and wear, since elements of the brake adjuster arrangement do abut against these sections, use these sections as an abutment as corresponding supporting or a bearing faces for movable components of the brake adjuster arrangement.
For that reason it is required to provide hardening and heat treatment to these internal surfaces. This connection, for example, also nitriding of these services is employed. Such hardening procedures are very costly. Moreover such hardening procedures require chemicals which have negative impacts on the environment and both on the safety and welfare of the workers during the industrial manufacture to a substantial extend.
The free end of the brake lever is connected with a rod of a pneumatic or hydraulic actuator in that a bold is passing through a hole in the upper lever section and a clevis of the actuator rod. The hole in the upper lever section is often reinforced in that a bushing is pressed into it which is able to provide a better wear resistance against the friction effects during brake actuation. Also this additional manufacturing step with the additional component is negatively influencing the overall costs of the manufacture of such a brake lever.